The present invention relates to a waveguide filter and method. More specifically, the present invention relates to a filter utilizing common waveguide elements, i.e. bends and media transitions, as the filter elements.
Waveguides are elongated hollow structures used for directing a high-frequency electromagnetic signal. Generally, it is desirable that the band of frequencies exiting the waveguide be the same as the band of frequencies entering the waveguide and great pains are often taken to insure that any impedance caused by a change in the direction of the waveguide and/or a transition in the medium are minimized. However, filtering to remove superfluous frequencies is desirable in many instances, e.g., where the equipment generating the electromagnetic energy may not be capable of generating a band of only the desired frequencies, or where the electromagnetic energy is the output of a mixer.
Filters for waveguides are well known. Typically, a filter comprises a number of voltage standing wave ratio (“VSWR”) elements having high reflection coefficients. When the elements are positioned approximately a half wavelength apart, a pair of elements creates a resonator that passes certain frequencies while rejecting others. A waveguide filter may require multiple resonators as a function of the amount of filtering being performed, i.e., the frequency response of each resonator is limited. In a typical millimeter wave filter, there are between five and nine, often seven, VSWR elements creating six resonators. Placing these in series along the axis of the waveguide typically results in a filter of approximately three inches in length, at about 38 GHz for example.
Where the electromagnetic energy is millimeter wave, size becomes very important. For example, it becomes problematic to enclose the transmitter and receiver in the same housing.
Other problems are encountered where the energy is being conveyed in a stripline on a printed circuit board and a media transition must be effected to mount the filter to the circuit board. Generally, compensation is provided for the impedance mismatch caused by the media transition requiring increasing the effective size of the filter.
Still other problems result from the presence of bends in the waveguide as may be required by the architecture of the system. Compensation for any bends in the waveguide increases the effective length thereof, making the size of the filter even more critical.
In one aspect, the filter of the present invention avoids the problems of the prior art filters through the utilization of common waveguide elements, i.e. bends and media transitions, as filter elements. The length of the filter may be reduced and the versatility of the filter increased by taking advantage of the characteristics of waveguide bends and media transitions and replacing the usual VSWR filter elements therewith. Additional size advantages are achieved by combining transitions and bends where the filter is attached to a printed circuit board and the use of bends, the existence of which is architecturally dictated, as filter elements.
It is accordingly an object of the present invention to obviate many of the above problems in the prior art and to provide a novel compact waveguide filter and method.
It is accordingly an object of the present invention to provide a novel waveguide filter and method that utilizes common waveguide elements as filter elements.
It is another object of the present invention to provide a waveguide filter and method for use with printed circuit boards.
It is yet another object of the present invention to provide a novel waveguide filter and method which facilitates the packaging of both transmitter and receiver into a common housing.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.